The role of siblings in development and adjustment has received less attention than the roles of parents or peers. Until recently, most of the research was primarily concerned with family constellation variables. In contrast, this project focuses on the qualitative features of the sibling relationship--i.e. the warmth, conflict, relative power, and rivalry in the relationship. A model is proposed in which such qualitative features are not only expected to be affected by constellation variables, but also by each child's relationships with parents, the relative quality of the two children's relationships with parents, the parental management of the sibling relationships, the martial relationship, the two children's social and personality characteristics, and the intermeshing of those characeristics. This project will develop new means of assessing these features, examine how the different factors in the model are associated with individual differences in sibling relationships, and examine how sibling relationships differ from other relationships. Six studies are planned. The first study examines the relations among parent-child relationships, parental management of sibling relationships, marital relationships, and school-aged children's sibling relationships, using questionnaire, interview, and observational data. The second study addresses similar issues in a sample of preschool children. The third study compares and contrasts relationships with handicapped and nonhandicapped siblings and examines the variation in such relationships. The fourth study examines the role of individual children's characteristics and the intermeshing of such characteristics. The fifth study examines twins' and closely-spaced siblings interactions with each other and friends. The final study compares children's interactions with older siblings and parents. Thus a range of topics will be studied, using a number of different methodological approaches. The findings should lead to a better understanding of the nature of sibling relationships and their role in the social network.